Conventionally, thermal printers are known in which energization of heater elements provided to a thermal head is controlled for desired printing onto a printing medium. Such a thermal printer is described in, for example, Unexamined Japanese Patent Application Kokai Publication No. 2011-126140.
If the heater elements are continuously heated during an energization period, the temperature of the heater elements will significantly rises. When the peak temperature of the heater elements becomes too high, a phenomenon called broken ribbon in which an ink ribbon melts and breaks or a phenomenon called sticking in which the thermal head sticks to the ink ribbon or the printing medium may occur and then the print quality may deteriorate.